The long term goals of this project are threefold; to understand gene regulation, particularly of a locus situated in heterchromatin, to understand the development of functional sperm, and to understand the organization and evolution of the eukaryotic genome. The specific aims of the proposal are: 1) to further characterize the X-linked Stellate locus of Drosophila melanogaster (which affects the morphology of proteinaceous crystals found in abnormal XO spermatocytes) and its Y-linked cognate (which controls the level of expression at the Stellate locus) by genomic Southerns to identify unique hybridizations sites of cloned DNA and S1 nuclease mapping of the transcription units within the region; 2) to determine if the XO crystal protein is the gene product of the Stellate locus using monoclonal antibodies raised to spermatocyte proteins; 3) to probe the spatial and temporal expression of the Stellate product in normal XY spermatocytes using the same monoclonal antibodies; and 4) to survey the range and geographical distribution of natural variation at the Stellate locus in widely dispersed populations Drosophila. By phase contrast microscopy and quantitative genomic Southerns. An explanation of the regulation and function of a locus expressed during spermatogenesis and regulated by the Y chromosome can help in understanding normal gametogenesis in particular and gene regulation in general. Such knowledge is important for the understanding of genetically based developmental and metabolic disorders and for their eventual diagnosis, treatment and prevention.